Step #1 Preheat the oven to 375 degrees F, then grease & flour two 9" round cake pans.
Step #2 Sift or whisk together the flour, baking powder & salt, then set aside.
Step #3 In a large mixing bowl, cream the butter, then slowly add the sugar, mixing well.
Step #4 Add the eggs one at a time, beating well after each is added.
Step #5 In another bowl, mix together the orange juice & zest.
Step #6 To this orange mixture, then 1/2 the liquid mixture, alternate adding 1/2 the dry mixture, & repeat, mixing well.
Step #7 Add this final orange mixture to the creamed butter mixture & mix well.
Step #8 Pour the batter into the prepared cake pans & bake for 30 mins.
Step #9 Cool in the pans on a wire rack for 10 mins, then remove this from the pans & cool completely.
Step #10 For the frosting, melt the butter, then mix it with the orange juice & zest, beating well.
Step #11 Slowly add the powdered sugar & beat well.
Step #12 Place one cake layer upside down on a serving plate &, frost the first layer, using less than 1/2 of the frosting, staying at least 1 1/2 inches from the edge.
Step #13 Put the second layer upside right on the bottom layer, pushing down lightly to secure it.
Step #14 Frost the top of the cake, allowing some of the frosting to run down the sides.